This invention relates to a plug container used in the introduction and separation of fluids in a well, such as the introduction and separation of cement slurry and displacing fluid in an oil or gas well. The plug container permits residue fluid, such as cement, to be cleaned from the plug container in response to a pressurized fluid lifting a bypass member and one or more plug holders disposed in the plug container.
Cement is used in oil or gas wells for various purposes. One purpose is to secure a tubular string (e.g., a casing or a liner) in the well bore. This is typically done by pumping cement down the tubular string and forcing it back up an annular space between the outside of the string and the well bore or a larger diameter string in which the first-mentioned string is disposed. To separate the cement slurry from drilling mud typically in the well when the cementing operation begins, a bottom cementing plug is placed in line and pumped down the string by the force of the following cement slurry. This bottom plug serves to minimize contamination of the cement as it is being pumped down the tubular string. It also wipes any accumulated mud film from the inner diameter of the string and pushes it ahead. To separate a following displacing fluid used to push the cement slurry out the tubular string and up the annular space, a top cementing plug is placed in line and pushed down the string by the displacing fluid. This top plug follows the cement and wipes any accumulated cement film from the inner diameter of the tubular string. It also prevents or reduces any contamination of the cement by the displacing fluid.
In wells drilled on land, surface-mounted plug containers are used in many cementing jobs to release the cementing plugs at the proper time. Normal job operations will have the bottom cementing plug loaded into the plug container prior to pumping cement. The top cementing plug will typically be loaded after the bottom plug is released. If well conditions dictate, two plug containers or a double plug container may be used to release both cementing plugs when desired without opening the plug container.
Subsea (ocean floor) completions are different from the aforementioned land-based cementing operations in that the cementing plugs used for separating the fluids are preferably located in the tubular string below the ocean floor. This is preferred because these plugs have a diameter large enough to wipe the inner diameter of the tubular string extending below the ocean floor, and this tubular string (and thus each plug) typically has a larger diameter than need be used for connecting this string with the equipment on the rig at the ocean's surface. Thus, the cement slurry is preferably pumped from the surface through a string of drill pipe smaller than the string being cemented, which smaller string extends between the surface rig and the downhole string to be cemented. This creates the need for a second type of plug container that houses elements, which may broadly be called "plugs" also, which are of smaller diameter to permit these plugs to pass through the narrower connecting string and into the downhole cementing plugs. A system using this technique is the Halliburton Energy Services' sub-surface release system ("SSR Cementing Plug Method"). This system provides a means of wiping different pipe sizes; therefore, smaller diameter drill pipe can be used as described instead of the larger diameter casing that otherwise would be run between the rig floor and the ocean floor.
This prior art system will be briefly explained with reference to FIGS. 1-3. These drawings schematically illustrate the sequence of operation.
FIG. 1 shows bottom and top cementing plugs 2, 4, respectively, installed at the top of casing 6 (i.e., the tubular string in the well bore) prior to beginning the actual cementing operation. A set of releasing pins attaches the bottom cementing plug 2 to the top cementing plug 4.
A weighted plastic or bronze ball 8 housed in a surface plug container 10 is dropped through connecting drill pipe 12 ahead of the cement slurry. The ball 8 passes through a wider axial channel of the top plug 4 and lands on a seat of the bottom plug 2. A differential pressure applied through the drill pipe 12 from the surface separates the thus sealed bottom plug 2 from the top plug 4.
FIG. 2 illustrates how the bottom plug 2 has been discharged from the top plug 4 and seated on a float collar 14 (or float shoe). At this point, a small increase in pressure exposes port holes in the plug 2 so that the cement slurry can be pumped around the bottom plug releasing ball 8.
A double collet releasing mechanism holds the top plug 4 in place and permits circulation through the top cementing plug 4 at normal displacement rates prior to release of the top plug 4. To release the top cementing plug 4, a top releasing plug 16 from the surface plug container 10 is pumped down the drill pipe 12 behind the slurry and into the top cementing plug 4 where it latches and seals therewith. An applied pressure shears releasing pins to enable the top plug 4 to move down the casing 6.
As shown in FIG. 3, the top cementing plug 4 lands on the bottom cementing plug 2 to shut off flow in conventional manner.
Another relevant prior system is schematically illustrated in FIG. 4. This represents the Halliburton Energy Services' selective release system ("SR Plug System"). This system makes it possible to perform a multiple stage cementing job on ocean floor completions or conventional land liner jobs using a Halliburton Multiple Stage Cementer and three plugs.
The SR Plug System comprises a first stage top plug 18, an opening plug 20, and a closing plug 22, all of which are located downhole as in the SSR Cementing Plug Method. These are respectively released by suitable drill pipe plugs initially contained in a surface/rig floor located plug container 24. The system is called selective release because it is designed so that the upper downhole plugs cannot be released until after the lower downhole plugs are released.
It is to the SSR Cementing Plug Method and the SR Plug System that the present invention is particularly directed. More specifically, the present invention is directed to the surface plug containers 10, 24. Although the foregoing systems have been successfully used, the surface plug containers 10, 24 have been of the manifold type as shown by manifold 26 in FIGS. 1-3 and manifold 28 in FIG. 4. Such manifolds have shortcomings. For example, if a fluid line is connected to a manifold, the manifold cannot be rotated. Valves are required in a manifold to direct fluid flow; these add weight, expense and maintenance to the plug container, and additional pressure lines are needed to operate the valves remotely. A manifold restricts flow area, and a manifold can cause the plug container to tilt off-center, making it harder to stab into casing or drill pipe.
Accordingly, there is the need for an improved plug container that can be used without the manifolds 26, 28 to overcome the aforementioned shortcomings.